The present invention relates to a process for improving the physical properties of granular detergents, and to be more precise, it relates to a process for improving the physical properties, particularly the caking property under pressure or a humid atmosphere, of non phosphate or low phosphate granular detergents containing a low percentage of phosphate, by making fine particles of calcium sulfite adhere to the surface thereof.
In the case of conventional granular detergents which contain a large amount of polyphosphates as principal inorganic builder, on account of the characteristics of the polyphosphates builder, the powdery properties thereof, such as the free flowing property and the ability to prevent caking due to moisture adsorption, and compression, etc., are satisfactory and no particular troubles have been encountered. However, since a demand for reduction of the phosphorus content of detergents has grown in recent years, the circumstances have greatly changed.
As a builder replacement for phosphates, sodium silicates, carbonate or bicarbonate have held an important position in the art. However, although these substances are admittedly capable of fulfilling the function as a builder related to detergency, their efficiency for imparting satisfactory physical properties to the granular detergent is inferior to the polyphosphate builders. Consequently, they have the drawback that they produce granular detergents having poor physical properties and therefore they cannot practically be used in large amounts. As the art of improving the caking property due to moisture absorption with respect to non phosphate or low phosphate granular detergent, there are known various processes for improving the characteristics of the surface of the granular detergent by covering the exterior of the granulated detergent with some non-hygroscopic builder, metallic soap or water-insoluble substance (cf. U.S. Pat. Nos. 3,950,275, 3,925,266 and 3,989,635). However, although all of these known processes are admittedly effective in preventing the caking of the granular detergents owing to moisture absorption, they have not always been satisfactory because they involve various shortcomings such as the complexity of process, the difficulty of obtaining homogeneous products, the solubility of the detergent, the caking characteristic at the time of storage over a long period of time, and so forth.
The inventors have conducted a series of studies on fine particles insoluble in water and/or slightly soluble in water which might be usable as a surface characteristic improver for granular detergents and have come to a finding that calcium sulfite would display an excellent efficiency in improving the physical properties of granular detergents and particularly in disintegrating agglomerated detergents which solidify under a slight pressure, such as the dead load of the detergent per se, owing to moisture absorption to the initial state of the granular detergent, or the so-called "caking preventability by compression at the time of absorbing moisture." The present invention has been accomplished on the basis of this finding.